Defects & Errors

Every production process is facing defects. Small defects or large defects, recurring or one-time defects, they are inherent to production processes. Today’s manufacturing challenge is to reduce these defects to decrease costs and increase customer satisfaction.

Below the difference is explained between defects and errors.

Defects

A defect is a non-conformity when comparing the result or output to the customer requirements. Defects can arise due to 3 different reasons:

Defects

because of a difficult process

because of variation in the process (environment, material, equipment, measurements)

because of errors or human mistakes

Difficult processes can be simplified. Variance in the process can be reduced by means of Statistical Process Control (SPC) and errors should be addressed by implementing a poka-yoke.

Errors

An error is an inadvertent, unintentional mistake caused by a human/an operator, which can result in a defect.

Daily-life examples are:

Forgetting the keys in your car
Time – Money – Safety – Reputation

Forgetting to pull out the plug

Running out of gas on the highway

Manufacturing examples are:

Forgetting to apply a felt

Forgetting to tighten a bolt

Applying the wrong component

Errors are a waste as they reflect loss oftime, money, reputation and above all can have an impact on safety of the operators and the customer.

Why do errors occur?

As human being it is normal to forget something or make a mistake. We see this in our daily lives, so why would it be different in a manufacturing environment? Too often the operators are blamed for the mistake, but actually the system should be build in such a way that it is impossible to make the mistake in the first place.

Error classification

As a result, we can classify errors in subgroups.

Errors

Processing or operation errors: a process operation is incorrectly executed. The process is not executed according to the standard. e.g. the bolt is not fully tightened.

Missing part errors: a component is not assembled, e.g. only four out of five bolts are tightened.

Setup errors: the wrong tools or machine settings are used. Incorrect adjustments are made, e.g. a bolt is tightened with an ordinary wrench instead of a QL-wrench.

Omitted processing errors: a process operation is missed.

Wrong part errors: an improper part is selected to assemble, e.g. a 5 mm instead of a 4 mm bolt is selected.

Misassembled parts errors: a part is assembled incorrectly, e.g. a bracket is mounted upside down or a bolt is tightened upside down.

Measurement or adjustment errors: a mistake was made in the measurement of a part, like measurements incoming parts, measurements on the machine settings, e.g. hole size is wrong.